1. Field of the Invention
This invention relates to substantially anhydrous complexes of polyvinylpyrrolidone (PVP) and hydrogen peroxide (H.sub.2 O.sub.2), and, more particularly, to a semi-anhydrous, suspension process for preparing such stabilized complexes as uniform, free-flowing, fine, white powders containing about 18 to about 22% H.sub.2 O.sub.2.
2. Description of the Prior Art
In the copending U.S. patent application, water soluble or insoluble PVP powder containing about 4.5% water is suspended in anhydrous ethyl acetate and an anhydrous H.sub.2 O.sub.2 solution in ethyl acetate is added thereto. Upon mixing, a fine, white powder is obtained, which is filtered and dried in vacuo to remove residual solvent. The product is a stable, substantially anhydrous complex of PVP and H.sub.2 O.sub.2 in the form of a uniform, free-flowing, fine white powder having an H.sub.2 O.sub.2 content between about 13% and 23%. This process, however, requires the use of anhydrous H.sub.2 O.sub.2 in ethyl acetate which is difficult to prepare and to handle safely.
Shiraeff, in U.S. Pat. Nos. 3,376,110 and 3,480,557, discloses a solid, stabilized hydrogen peroxide composition of hydrogen peroxide and a polymeric N-vinyl heterocyclic compound prepared in an aqueous solution of the components. These compositions generally were prepared by mixing various weights of PVP and aqueous H.sub.2 O.sub.2, and evaporating the solution to dryness. The Shiraeff composition, which was believed to be a solid, dry complex, was described as not necessarily anhydrous due to the hydrophilic nature of the PVP and the water present in the reaction solution. Shiraeff further stated that such amounts of water could be tolerated, however, if it did not affect the solid dry characteristics of the complexes. The H.sub.2 O.sub.2 content of the composition was given as being at least 2%, and preferably 4.5 to 70% by weight. Prolonged drying to remove water from such compositions, however, resulted in loss of H.sub.2 O.sub.2 forming a brittle, transparent, gummy, amorphous product. In U.S. Pat. No. 3,480,557, the aqueous PVP-H.sub.2 O.sub.2 complexes, upon heating to dryness, produced hard, brittle chips which had a variable H.sub.2 O.sub.2 content ranging from about 3.20 to 18.07% by weight, depending upon the drying times.
Accordingly, it is an object of this invention to provide a process of making stabilized, substantially anhydrous complexes of PVP and H.sub.2 O.sub.2 as a uniform, free-flowing, fine, white powder containing about 13% to 23% H.sub.2 O.sub.2 which does not require the use of anhydrous H.sub.2 O.sub.2 solutions.
A particular object herein is to provide a suspension process using only 70-85% H.sub.2 O.sub.2 aqueous solutions for making substantially anhydrous, uniform, free-flowing, fine, white powder complexes of PVP and H.sub.2 O.sub.2 having a H.sub.2 O.sub.2 content between about 18 to about 22%.